To dupe: block the two packets that are sent when you close the client (they're save and exit server packets). Your char will be stuck on the server for an hour or so till it gets booted. In the mean time you can keep relogging in and handing your items off over and over again. Lots of other ways to dupe, this is just the easiest example.
Account hack: when you select a server you send a packet with your account name and a password hash. Change the account name to the person's account which you want to log into and change the password hash to anything, like "SSSSSSSSS" and you'll log into their account. You can also get into banned accounts this way.
Atheuz' old level/money hack wasn't really patched either, only the client was. You can either edit the .exe to bypass it, replace the patched quest_reward.tb (or whatever it's called) in the program's memory with an old one, or use an old client with old table files to get past the client patch.